1. Field of Invention
The present invention relates to a wireless base station for communications network, the base station having a plurality of wireless communication media each providing a communication area.
2. Description of Related Art
In recent years, a variety of wireless communication systems have come to be in broad use, with the users demanding increasingly greater variety of data communications and higher transmission rate. Under the circumstances, there is a greater demand for higher spectral efficiency in wireless communication systems. One of the known wireless communication systems with improved spectral efficiency is cognitive radio communication system. A cognitive radio communication system is adapted to recognize radio environment of the wireless communication station to perform communications through optimal wireless communication media and optimal channel. A cognitive radio communication system is capable of enhancing spectral efficiency through the selection of optimal media (frequency) on the basis of the recognition of the quality of radio environment. A cognitive radio communication system can be used, for example, as a temporary back-up system network in extraordinary emergency such as a great earthquake and tsunami. More specifically, when ordinary communication systems have been knocked out of service due to such serious disaster, a mobile base station adapted to cognitive radio communication can be brought in to quickly provide a wireless communication system to secure communication network. As stated above, a wireless base station for cognitive radio communication is adapted to recognize radio environment surrounding it and establish self-controlled communication link with optimal wireless media to the recognized environment. Thus, a wireless base station for cognitive radio communication can be quickly set up upon suffering disaster, without any need for advance study on the location of such base station.
Since a cognitive radio base station selects wireless media on the basis of the quality of radio environment, such environment should preferably be predicted as of a future point in time where the wireless media is actually used. As a conventional technique of predicting the radio environment, PCT International Publication No. WO 2004/109536 A1 is cited. In the approach adopted in the PCT Publication, the prediction is based on signal strength, signal-to-noise ratio or any statistic collected at physical layer, which is deemed representative of link quality. In addition, the predicted value is adjusted on the basis of the traffic conditions (e.g., idle, light traffic, moderate or heavy traffic) being experienced by the node whose link qualities are being estimated.
However, the above-mentioned conventional method for predicting the radio environment involves the problem such that neither prediction error nor importance of message is taken into account and consequently that it is difficult for the base station to select wireless media suited thereto with prediction error and/or importance of message taken into account.
With a view toward resolving the above problem, the present invention is aimed at providing a wireless base station, which is capable of selecting wireless communication media suited optimally for the current state thereof and for the current state of radio environment, by providing correction to the predicted value on the basis of the importance of message and traffic load being experienced by the base station while achieving improvement in spectral efficiency.